A citation analysis of chemistry PhD dissertations at the University of Texas at Austin yielded data on how often graduate students cite books in their bibliographies, and on the characteristics of the books cited, in terms of age and local ownership. The analysis examined samples of dissertations selected from five discrete years--1988, 2006, 2009, 2012, and 2015--in order to provide longitudinal data on how citation trends are changing during a transition period in libraries. Data indicated that chemistry graduate students cited low numbers of books relative to journal articles, confirming expectations from similar studies, and that the trend over the time period studied is downward, despite the increasing number and availability of e-books. The results could inform collection management decisions and strategies for promoting book content to graduate students in future.